Freezing point depression is a colligative property observed in solutions that results from the introduction of solute molecules to a solvent. The freezing points of solutions are all lower than that of the pure solvent and is directly proportional to the molality of the solute.
ΔTf=Tf(solvent)−Tf(solution)=Kf×m
Δ
T
f
T
f
s
o
l
v
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n
t
T
f
s
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t
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K
f
m
where ΔTf
Δ
T
f
is the freezing point depression,Tf
T
f
(solution) is the freezing point of the solution, Tf
T
f
(solvent) is the freezing point of the solvent, Kf
K
f
is the freezing point depression constant, and m is the molality.